Monoethylene glycol is used as a raw material in the manufacture of polyester fibres, polyethylene terephthalate (PET) plastics and resins. It is also incorporated into automobile antifreeze liquids.
Monoethylene glycol may be prepared from ethylene oxide via ethylene carbonate. This is typically carried out in a two-step process wherein the first step is the reaction of ethylene oxide with carbon dioxide to form ethylene carbonate, and the second step is the hydrolysis of ethylene carbonate to form ethylene glycol.
U.S. Pat. No. 6,187,972 describes a process for manufacturing ethylene glycol from ethylene carbonate wherein the hydrolysis is carried out in two reactors. In an example, the conversion of ethylene carbonate achieved in the first reactor is 93.0% and in the second reactor is about 100% (the detection limit was less than 10 ppm). It is desirable to minimise the amount of unreacted ethylene carbonate that remains in the ethylene glycol product because the compounds form an azeotropic mixture and their separation and purification is difficult. A similar process for manufacturing ethylene glycol is disclosed in U.S. Pat. No. 6,080,897.
The present inventors have sought to further improve the manufacture of alkylene glycol from alkylene carbonate, maximising conversion and minimising liquid shortcutting whilst ensuring that the process is as economical as possible. In practice, decreasing the residence time of the reactants and/or decreasing the reactor size can increase the economy (i.e. minimise the cost) of the process. The present inventors have therefore sought to provide an improved process wherein the conversion to alkylene glycol is maximised (and is preferably 100%) and liquid shortcutting is avoided whilst maintaining or decreasing the residence time and/or the reactor size.